The invention relates to methods of and to apparatus for manipulating stacks of paper sheets or other block-shaped commodities. More particularly, the invention relates to improvements in methods of and in apparatus for manipulating block-shaped commodities in production lines, such as those wherein stacks of paper sheets are draped into blacks of wrapping material prior to introduction into boxes or like receptacles.
Commonly owned U.S. Pat. No. 4,683,704 to Vorachek et al. discloses a method of and an apparatus for manipulating sheets of paper or the like in a sheeter (namely a machine which accumulates sheets of paper or the like into stacks) and in a wrapper which receives stacks from the sheeter. More particularly, the patent to Vorachek et al. discloses a method of and an apparatus for synchronizing the operation of a sheeter with that of a wrapper. Stacks of sheets which are advanced from the sheeter into the wrapper must be transported along an elongated path, and the arrival of stacks into the wrapper must be properly timed to ensure that each stack will reach the wrapping station during a predetermined phase or stage of the respective cycle of the wrapper. This necessitates the provision of a satisfactory infeed apparatus which can control the advancement of successive stacks toward the wrapping station. The stacks are normally advanced by a series of successive endless conveyors each of which comprises several discrete tapes trained over pulleys and being driven to advance the stacks along the elongated path. The transport of stacks often results in at least some shifting of certain sheets relative to the other sheets in a stack so that the stacks can develop so-called tails, namely, groups of lowermost sheets which are shifted relative to the sheets above them. A tail extends from the rear end face of the respective stack, and its sheets are likely to be damaged or defaced during transport toward the wrapping station. Such transport normally involves engagement of the rear end faces of successive stacks by discrete flights of a transfer conveyor which serves to advance successive stacks at predetermined intervals in order to ensure that the stacks will reach the wrapping station during the aforementioned phase or stage of the respective wrapping cycle.
Additional problems arise during transport of stacks whose orientation deviates from an optimum orientation. The misoriented stacks must be reoriented in order to ensure that their front and rear end faces will extend exactly at right angles to the direction of transport not later than when the stacks approach the wrapping station. Presently known orientation changing means include a pair of rollers or drums which are installed at the upstream end of a channel wherein the stacks advance toward the wrapping station while being engaged by the flights of the aforementioned transfer conveyor. A drawback of rollers or drums is that they are likely to lock a stack at the inlet of the channel if the actual orientation of an oncoming stack deviates excessively from the desired or optimum orientation.
The patent to Vorachek et al. discloses an elevator which is provided at the wrapping station to move successive stacks from a first to a second level while the stack is in the process of being draped into a blank of wrapping material. This involves conversion of the blank into a tube which surrounds the stack on the elevator, and closing of the ends of the tube by suitable tucking and folding instrumentalities in order to convert the tube into a prismatic envelope which completely surrounds and confines the respective stack. Problems arise when the stacks are wrapped at a high frequency because the marginal portions of a blank, which are to overlie each other, in order to convert the blank into a tube, are likely to be flexed and/or otherwise deformed by currents of air at the wrapping station.